Some history. I only have three gassers. One is new so I don't know how it's going to be. Have a DA-60 that has given me zero problems. Finally I have a DLE-30 that just ate it's 2nd throttle servo. I am just using plastic geared $15 servos. Ball links on both ends with metal push rods.I have removed the return spring and set the end points on the 10C radio where it's never in a bind. One exception might be when I use the throttle cut function to shut it down, but it's not a hard pull and it would only stay thay way for a second or two.
Neither of these servos has broke a gear, the problem is in the circut or signal to the servo. Both would start to blip the throttle in flight for no reason or go the other way and kill the motor. The second servo only lasting 12 flights or so.
So do I need to upgrade throttle servos on all the gassers? Did I just happen to get a couple bad Futaba servos? I am at a loss as to why these would both do the same thing when there is almost no load on them.


Thanks, David

Futaba standard nylon gear S3004 servos on all throttles, glow and gas.

S9101 for me. Sullivan Nyrods. No problems. 50cc gas. Servos just wear out over time. Usuallly the feed back pot. Dan.

Ditto ! Have used Futaba and Hitec standard servos with no problems.

Perhaps it has more to do with where and how the throttle servo is mounted which you didn't say. Loosing two throttle servos is a bit unusual, actually quite a bit unusual.

I have room to move it back Pam. Right now it's next too the front of the tank. About 5" from the carb but inside the fuse.

David

I've always used the 3004 servos on throttles ever since that servo came out.

I wonder then if the metal pushrod is transfering vibrations to the servo, especially with a short pushrod. You might just replace the metal rod with a nyrod in between the ball links which should isolate it somewhat from vibrations.

I use the Futaba 3003 or 3004 servos, nothing fancy.

Now sometimes the throttle return spring may be too stiff and that could stress the servo causing the driver transistors to fail. Some guys use a thin wire to pull the throttle and let the spring return it. So in that case you don't want the return spring to be too stiff. Using the stock short throttle arm can be a problem as there is little leverage against the spring which makes the servo work harder too. If you have the spring on the throttle with the pushrod that opens and closes the throttle, you can pop the spring end off and leave it on there as a spacer and see if that fixes the problem for you or not.

If the airframe isn't very rigid in relation to the engine, the excessive engine movement can cause a stiff pushrod to strain the servo causing it to fail in the same manner. You basically have the engine vibration beating up on the servo via the pushrod then. So using a flex cable or golden rod might do the trick in that case too.

Not sure I can make myself put Nyrod in a plane :-)

May have to try it though. It sounds like I am doing everything else right. I have a Du-bro heavy duty arm on that servo also. If vibration is the issue a stock arm should help with that. The two servos in question were 3004s. This is a 3DHS Edge 540 and it is built really light. It does rattle the covering when I putt around so I know the airframe is getting a lot of vibratio

Plan of action wil be to order a little better servo ( can get a digital for $10 more than the 3004), switch to a plastic pushrod, and might as well balance the Xoar prop while it is all apart. I don't remember if I checked it when I put it all together or not.

Thanks all. I will find this thread and post back if I have more problems with the servo.

david

Dave, you better check around to find out if a digital servo is what you need for throttle. Maybe some guys watching this can comment on it. Dan.

For years I've always used ball links with 440 threaded rod on 3004,3151 and a bunch of other cheap and expensive servos and never had any problems. Are you sure there is no binding
somewhere?

Bill

JR DS821 in my TopFlite GS Corsair and GS P51

I think the vibrations are the cause of the servos failing. Move the servo back ... further away from the engine.

Contrary to what the Beach Boys think ... vibrations are not good.

I know you can't avoid them in gassers, but those long and short wave vibrations will also destroy the structure. Dampen them as much as you can.


As for me, I use Futaba 3010 ... even an old S148 (never failed me yet).

You can also try gluing in a separate servo mount using a thick bead of silicone to further isolate the servo. Make sure you aren't squashing the grommets too much. That's the biggest mistake I see when people mount servos. Second most common mistake I see is the eyelets upside down or just missing.

3004 futaba, use them allot for about everything"

Are you sure it's not rf coming down the metal pushrod? Are you on 2.4
A nyrod will stop vibrations as well so I would use that.

I concur. The symptoms sound like RF to me.

try using a Castle. No linkage...no problems!

I mostly us nylon gear Hitec or what ever I have around the shop from retired aircraft................I purchased a couple of throttle servos and was glad to see hitec make a new HV430 an upgrade on the old 425, to high voltage 7.4V..... works out great on all my gas Life batt setups

David - sounds a lot like you have some kind of electronic interference issue. Are the two servos you've had trouble with the only ones you have had in that airframe? If yes, then I would most definitely go searching for an RF related issue. In my many years of doing these, I've found and heard of so many different servos that *do* work on gas engine throttles, that I tend to pretty much dismiss a servo issue initially. Look elsewhere, particularly if servo is anywhere physically near a kill switch, or ignition battery, or ignition, and if you are on 72Mhz, it could be practically anything metal-to-metal on the airframe ANYPLACE creating throttle blips like you describe.

Well since you say they are "GS" I'll ask if they are gas powered too? If so, you crap out on several points buy using those servos which are not recommended for gassers or anything over, IIRC, 11 lbs. Horizon had lots of grief with those servos and the Spektrum DS821 which is the same servo, when they started inlcuding them with radio sets and people didn't bother to read, or didn't believe the warnings. Vibration, fatigue and the output shaft snaps off....

As for me, my current favorite throttle servo is a Hitec 7985. Digital, MG, high resolution, programmable and pretty damn fast. Works great on the gassers.

+100, Zeeb.

I always use nylon geared standard BB.

I have had the same problem you seem to have. Later testing of the ofending servos out of the plane proved the servos were fine.

RF was the problem. Better isolation of the ignition or a differnt ignition was the solution.

While I've used my share of low cost servos for throttle and without problems I might add, over the last several years I've migrated to better quality ones. I've heard it stated that if you wouldn't trust a particular servo on a flight surface, you shouldn't use it on the throttle. I think that statement has some merit and especially if you don't have a radio controlled ignition cut off of some sort. Most of my throttle servos are now high quality, low time, retired collective servos from helis.